It's pretty simple really. If you use the software provided from Ustream it is drop dead easy. I would just advise you to do plenty of testing before the event as something always needs tweaking it seems.
There are a couple of free to use software packages that give you some flexibility with your stream. As I am a noob with this as well I would not feel comfortable trying to support you with information. But if you are any kind of geek you will figure it out easy enough.
http://obsproject.com/ and
http://www.xsplit.com/
I recommend Open Broadcaster. It is not as fancy but it is more stable than Xsplit.
You can see what I have done at
http://www.justin.tv/0kie/videos and
http://www.justin.tv/jamaicajoes/videos
Good luck with it!
Ken